The invention relates to a process for the recycling of nuclear fuels contained in a first metal can, within which said pellets have previously been irradiated in a fast neutron nuclear reactor.
In fast neutron nuclear reactors, the fissile material is in the form of pellets, normally constituted by a mixed uranium and plutonium oxide (UO.sub.2, PuO.sub.2). These pellets are stacked within metal cans to form the nuclear fuel rods. These rods are arranged in bundles in sleeves with a hexagonal cross-section, so as to form nuclear fuel assemblies.
When a new assembly is placed in a fast neutron nuclear reactor core, there is a certain radial clearance between the nuclear fuel pellets and the cans containing said pellets. This initial clearance is provided to take account of the swelling of the pellets occurring under irradiation and to ensure a satisfactory introduction of the oxide pellets into the can during production.
Moreover, the irradiation time of the assemblies in the core of a fast neutron nuclear reactor is limited by the deformation undergone by the fuel rod and the hexagonal tube, said deformations being essentially caused by the swelling of the steel.
In the present state of the art, the nuclear fuel assemblies are then dismantled, the rods cut up and the fuel removed. These operations obviously take a long time and are very expensive, the latter particularly penalizing the costs of the fuel cycle of fast neutron nuclear reactors.
The present invention is based on the observation that when the irradiated assemblies are removed as a result of the swelling of the cans, the combustion level of the fuel pellets is low compared with the combustion possibilities intrinsically offered by said fuel.
In the particular case of a fast neutron clear reactor comprising a zero reactivity drop core, such as is proposed in French patent applications Nos. 84 12123 and 85 01203, reprocessing would be considerably spaced if the irradiation time of the assemblies was not limited by the swelling of the cans.
It would therefore appear that the limitation of the irradiation time of the assemblies imposed by the swelling of the cans leads to a mediocre exploitation of the possibilities offered by the actual fuel. In particular, the reprocessing of the fuel after a single irradiation period of limited duration is not justified and considerably increases operating costs.